Crouch-walking made the legs glitch through the body. The first fix put the feet on the ground correctly, but from the side the character was kneeling rather than crouching, so it was rejected.
A diagnostic showed the leg solver was doing its job: the feet reached their targets. The problem was upstream. The hips were placed so that the only way for the feet to reach the ground was to fold the knees down. Moving the crouched pelvis back by 25 cm and adding a forward lean produced a supported squat, checked against 34 matched shots.
Later that day, seven full-body crouch animations replaced most of the hand-tuned posing. A small foot jump on sharp changes of direction remained. The mannequin was a stand-in; the survivor replaced it in third person two days later.